The present invention relates generally to cardiac pacing. More particularly, the invention describes novel devices and methods of physiologic cardiac stimulation using a multi-electrode cardiac pacemaker configured for stimulating ventricular intraseptal area of the heart engaging the natural conduction pathways in the cardiac septum.
His bundle pacing has emerged recently as a useful alternative to traditional single- and multi-chamber pacemaker configurations, especially as a good physiologic alternative to right ventricular pacing. In studies, His bundle pacing has been shown to be associated with a significant reduction in mortality as well as various complications such as heart failure hospitalizations and upgrade to bi-ventricular pacing in comparison to right ventricle pacing in patients with bradycardia and indications for permanent pacemakers (see for example Sharma PS, etc. Permanent His bundle pacing is feasible, safe, and superior to right ventricular pacing in routine clinical practice. Heart Rhythm. 2015; 12(2):305-312). Based on a systematic review of the available published literature on physiologic pacing. HBP was incorporated into the recently released 2018 American Heart Association/American College of Cardiology/Heart Rhythm Society guidelines on the evaluation and management of patients with bradycardia and cardiac conduction delay.
At the same time, while His bundle pacing is feasible in the majority of patients requiring ventricular pacing, it may be more challenging to implement in some patients due to existence of high capture thresholds or an inability to correct underlying His-Purkinje conduction disease (see for example Vijayaraman P. His bundle pacing to left bundle branch pacing: evolution of His-Purkinje conduction system pacing. The Journal of Innovations in Cardiac Rhythm Management, 2019; 10:3668-3673).
FIGS. 1 and 2 illustrate that this can be explained by the position of the source of conduction abnormalities 22 located distally of the AV node 10 and His bundle 20. FIG. 1 shows the right atrium and intraseptal conduction pathways and FIG. 2 shows how conduction pathways bifurcate distally of the His bundle into right bundle branch 12 and left bundle branch 14, which in turn also splits into Left Posterior Fascicle 16 and Left Anterior Fascicle 18.
To overcome this condition, pacing of left bundle branch 14 and/or right bundle branch 12 at locations distal of the conduction abnormality 22 may be implemented by positioning the pacing electrodes at the intraseptal area of the heart between the right ventricle and left ventricle, see for example positions 12 and 14 in FIG. 1 as examples of such locations.
As discussed in my earlier patent applications, deployment of a pacing electrode aimed to reach intended conduction fibers such as His bundle and provide for pacing with a low capture threshold may be difficult to achieve. Multiple placements of such electrode may be attempted before achieving a satisfactory result. The need therefore exists for devices and methods for improved deployment and operation of cardiac pacemakers configured for stimulation of left and/or right bundle branches of the heart at a location defined by the heart interventricular septum representing a target, which may be easier to reach with a single deployment.
A further uncertainty during deployment of a conventional electrode when used for intraseptal pacing is the location of the conduction fibers for one of both branches of the His bundle. For each branch, it is uncertain as to where the fibers are located so as to minimize the capture threshold. This location uncertainty may be divided into a lateral position uncertainty (radially away from the center of the delivery system) as the electrode is approaching the septal surface and a depth uncertainty as such conduction pathway fibers may be positioned at various depths inside the septum of the heart.
Septum thickness is limited as well as electrode deployment would be done best if it does not protrude/perforate across the septum and emerges on the opposite side of the septal wall. Anatomical variations between subjects may make if difficult to design one or just a few sizes of such electrodes for use with most subjects.
The need exists therefore for a universal design of intraseptal pacemaker configured to be used in most cases without the risk of “under-deployment” or “over-deployment” into the septal tissue.